Electromagnet controls for sheet handlers



R. B. POWERS 2,895,733

ELECTROMAGNET CONTROLS FOR SHEET HANDLERS 3 Sheets-Sheet 1 July 21, 1959 Filed April 10, 1956 INVENTOR. Robert 8. Powers 8C 5 N I ISATTORNEYS July 21, 1959 R. B. POWERS ELECTROMAGNET CONTROLS FOR SHEET HANDLERS Filed April 10, 1956 .3 Sheets-Sheet 2 1 ulllllllllllllllllllnllI I I I I l I I l l l I l a l I I Ill r lllllll II INVENTOR Robert 8 Powers QC M,

HIS ATTORNE Y5 0w 3 mm TmJ July 21, 1959 R. B. POWERS ELECTROMAGNET CONTROLS FOR SHEET HANDLERS Filed April 10, 1956 5 Sheets-Sheet 3 s s 4 4 a 02,. n mw N m m V mm w 8 r A 4 T m M Ms 0 m 5 R United States Patent ELECTROMAGNET CONTROLS FOR SHEET HANDLE-RS Robert B. Powers, Columbiana, Ohio, assignor to L. W. Nash Company, East Palestine, Ohio, a corporation 'of Ohio Application April 10, 1956, Serial No. 577,309

9 Claims. (Cl. 271-18) This invention relates to magnetic sheet handlers for feeding individual metal sheets to conveying or processing machinery and more particularly, it relates to controls for the electro-magnets in the handler which manipulate the sheets by magnetism.

Magnetic type sheet handler machines are arranged to receive the sheets in a stack and have two types of electro-magnets which cooperate to separate the sheets from the stack one at a time beginning at the top. The primary type or family of electro-magnets in the machine presently contemplated has three phases of operation. First, this type electro-magnet is deenergized until there is only a narrow gap between it and the top of the stack. Second, the electro-magnet is energized for a second phase in its cycle of operation and the top sheet lifts through the gap under the magnetic strength of the electro-magnet to separate by a distance approximately less than 1 inch from the stack. Third, this family of electromagnets exerts magnetic forces holding the lifted sheet away from the stack and only part strength is required to hold this sheet as compared to the full lift strength previously required. An unwanted tendency of this family of magnets is that if they remain energized at full strength and one or more becomes exposed following the second phase of their operation, for instance exposed by being uncovered by the sheet as its shifts in its own plane to be conveyed away, then the uncovered magnets immediately tend to cause the next sheet on the stack to lift. Such a localized lifting force is naturally uneven so far as the whole surface of that next sheet is concerned and at best the lifting cannot be uniform on the sheet which therefore would not be level as it rose but would whip upwardly or otherwise rise in an irregular fashion.

The other type electro-magnet is a rifller magnet which functions primarily during the second phase of operation just noted. The individual sheets are sometimes oily or otherwise tend to stick to the stack and thus resist being separated therefrom. The rifiler magnet cooperates with the first magnet in turning one edge of the top sheet so as to break the cohesion between that sheet and the rest of the stack and thereby free it for its lifting motion upwardly. An unwanted tendency of the rifiler magnet is that if it remains energized, it tends to reattract the captive leading edge of the sheet from the first magnet, particularly as the leading edge of the sheet transfers subsequently in a direction over the rifiler magnet.

A primary object of the present invention is to provide, in a machine such as the foregoing, a system of switching elements and mechanism controlled thereby which times the operation of the electro-magnets in the machine at various stages and renders the magnetic handling operations essentially automatic. This system is especially adapted to free the machine from faulty operation due to the foregoing undesirable tendencies of the magnets. More particularly, the machine embodies an inverted bed of transfer rollers, and I provide magnet control switch mechanism including switches in this bed at strategic points which enable the magnet strengths to be varied ice and nullified at the proper time to control the sheets in rapid, trouble-free cycles of operation through the machine.

Further features, objects and advantages of this invention will be apparent from the ensuing description and from the drawings forming a part of this specification and which illustrate a preferred embodiment of the invention.

In the drawings:

Figure 1 is a plan view of the magnetic sheet handler machine embodying the present invention;

Figure 2 is a sectional view in elevation taken to enlarged scale along the lines II-II of Figure 1;

Figure 3 is a fragmentary enlargement of a portion of Figure 2;

Figure 4 is a schematic showing of the hydraulic power system for the machine;

Figures 5, 6 and 7 are sequential views schematically showing one cycle of operation of the machine; system for the magnets of the machine; and

Figure 8 is a schematic showing of an electrical wiring system for the magnets of the machine; and

Figure 9 is a modified form of electric wiring system for the machine.

In particular reference to Figures 1 and 2, a magnetic sheet handler machine is shown having a chain-driven transfer roller bed 10 (Figure 1) and an upright framework 20 incorporating a magnet and roller section 22 and a lift platform section 24 disposed below the section 22. The two sections 22, 24 are adapted to receive a stack S of individual metal plates or sheets from the transfer roller bed 10 and deliver them one at a time to a conveyor 30 which is diagrammatically shown and which either directly or indirectly transfers the sheets to processing machinery 40. Similarly to the transfer roller bed 10, the magnet and roller section 22 is chaindriven as will hereinafter be set forth more in detail and thus in one respect it constitutes an inverted transfer roller bed on the upper level at which it is arranged within the upright framework 20.

More particularly, the upright framework 20 is rectangular in shape and has an inverted U-shaped frame at each side thereof consisting of a pair of inner and outer columns 50 of I-beam construction which are connected at their upper ends by means of an angle member 52 and a channel member 54, Figure 2. A base plate 56 interconnects the lower ends of the pair of columns 50 in each U-frame and is suitably anchored to supporting masonry or to a concrete bed 57. The base plate 56 carries a set of leveling screws 58. The magnet and roller section 22 includes a pair of spaced cross beams 60 of channel-shaped construction which form bridging members between the U-frames, extending between the sides of the machine and being welded at their corresponding ends to the channel member 54 at that side. A series of short hanger bars 62 is welded to the upper edges of the cross beams 60 to form a frame in which each of the hanger bars 62 rigidly carries a U-shaped lift magnet core 63 provided with an electrical coil 64 on each of the salient poles 66 thereof. Below each coil 64, the salient pole carries a pair of spaced roller wheels 68 which rotate about a common fixed axis.

A stationary channel bar 59 is secured in a horizontal position to the opposite I-beams 50 in the inverted U- shaped frame at the discharge end of the handler. A U- shaped rifiler magnet core 61 is adjustably bolted to the channel 59 and carries an electrical coil on each of the salient poles 67 thereof. The coil and pole 65, 67 at each of the opposite ends of the core 61 cooperate in carrying a chafiing strip 69 of stainless steel which confronts the stack of sheets S so as to take up anywear caused by rubbing action of the stack from time to time.

The north one of the coils 65 is disposed adjacent the north one of the coils 64 for the lift magnet and similarly the south coils are arranged at corresponding ends of these magnets. Accordingly, the salient poles of the lift magnet core 63 are of like polarity with respect to the salient poles 67 of the riffier magnet core 61 and these magnets, though fixed, are mutually repellent of one another across the entire top edge of the stack S, Figure 2.

A series of driven conveyor rollers 70 is arranged in alternation with the pairs of roller wheels 68 which may also be power driven but as shown, are freely rotatable idler rollers and together the live and idler rollers 68, 70 cooperate to define a common horizontal plane for conveying sheets of metal along the underside of the section 22. A continuously driven pair of mutually op posed upper and lower pinch rolls is diagrammatically indicated at 72, Figure 2, in alignment with the plane of the underside of these rollers. These pinch rolls 72 keep the leading edge of the moving sheet in line with the conveyor 30 to which the sheets are fed regardless of whether the magnetic suspending force from the lift coils 64 thereafter partially or completely collapses. The cross beams 60 carry a series of bearing brackets 74 on their underside which journal the stub shafts 75 on which the conveyor rollers 70 are mounted. A chain and sprocket drive 76 interconnects the individual conveyor rollers 70 for coordinated driving movement together in the direction of the arrow 77, Figure l. A continuously run electric motor 78 is connected to drive the chain and sprocket drive 76 by means of a mechanical speed reducer 79 and an intervening chain and sprocket connection 80.

The motor 78 and the speed reducer 79 have a common chanel-shaped beam 81 which supports them and which bridges between the opposite cross beams 60. The beam 81 is vertically aligned with a smaller channel-shaped beam 82 on the underside of the cross beams 60 and cooperates therewith to define a guide for a switch actuating member 83. The switch actuating member 83 controls a pair of microswitch type limit switches LS-l, LS2 which are mounted to the beam 81. Another limit switch LS3 is mounted to the underside of the cross beams 60 so as to be disposed above the stack S. The limit switch LS3 is controlled independently of the switches LS-l, LS2 and has a downwardly protruding actuating finger sensitive to the presence of a sheet which has lifted through the gap and separated itself from the stack S.

At each of the four corners of the rectangular upright framework 20, the columns 50 carry a bracket 84 which rigidly supports a hydraulic lifting cylinder 86. Each of these four hydraulic lifting cylinders 86 has a vertically sliding piston 88 which divides the cylinder into lower and upper working chambers as viewed in Figure 2. A piston rod 90 extends through the lower working chamber and is connected at its upper end to the piston 88 and at its lower end the piston rod 90 carries a clevis and a pivot pin 92. The lift platform 24 is of rectangular shape and rigidly carries an apertured lifting lug 94 at each corner thereof which receives the adjacent pivot pin 92 so as to connect the platform 24 and each of the piston rods 90. The outer ones of the columns 50 carry a pair of vertically disposed racks 96 adjacent the ends of the platform 24. A stabilizer bar 98 is journaled at spaced points in a set of bearings 100 carried by the platform 24 and a pinion 102 afiixed to each end of the bar 98 meshes with the stationary rack 96 at that end. The bar 98 therefore interconnects the platform 24 and the stationary racks 96 in known manner and torsionally resists any tendency toward movement of the platform 24 out of its normally horizontal position, for instance, tilting movement due to unequal pulling of the piston rods 90 attended by unequal rotation of the pinions 102 as they travel along the racks.

The platform 24 has a plurality of parallel mounting brackets 104 on the upper surface thereof which carry two pairs of sets of freely rotatable conveyor rollers 106;

a stop 108 is suitably provided at one end of each pair of roller sets 106. The rectangular lift platform 24 which may be readily constructed from a box of frame members such as channel beams 110 is movable upwardly and downwardly by the cylinders 86 from a remote position in which the platform engages a stationary set of lower stops 112 into an upper position closely confronting the magnet and roller frame 22. During such upward movement, the rising rollers 106 carry the stack S toward the rotating rollers 70 until the gap between the top sheet and the rollers 68, 70 closes to less than approximately 1" whereupon the lift magnet coils 64 are automatically brought on at full strength'to cause the sheet to lift bodily through the gap. The holding strength necessary to maintain the sheet suspended against the rollers is only a fractional part, e.g. one-half, of the full strength of the magnets and is entirely inadequate to lift a sheet across the gap involved. Under these circumstances, a gap of /4" has been found to be very satisfactory.

In Figure 3 the switch actuating member 83 is square in cross section and is received at intermediate portions thereof to slide within complementarily square guide openings formed in the beams 81, 82 and vertically aligned with one another. At its lower end the switch actuating member 83 carries a feeler wheel 122 which is sensitive to the approach of the stack of sheets S. A bracket 124 welded to the member 83 carries a set screw 126 which engages the beam 82 to provide an adjustable limit stop for locating the feeler wheel 122 at the proper height in the machine. The upper end of the member 83 is also square but slightly reduced in cross section so as to define a diagonally outwardly extending shoulder or ramp 128 against which the feeler wheels 130 of the limit switches LS-l, LS2 rest. The coaction be tween the ramp 128 and the feeler wheels 130 of these microswitches LSI, LS2 is such that predetermined initial movement of the feeler wheel 122 of the order of .002" or .003" causes the switches to operate, with the switch LS-l being operated slightly in advance of the tripping of the switch LS2 under the gradually rising movement of the switch actuating member 83. Predetermined initial movement of the feeler wheel 122 causes the lift magnet coils 64 to be energized in a manner hereinafter more fully described and thereafter the feeler Wheel 122 is deflected by the lifted sheet into the dotted line position 122a in which it abruptly forces the switch actuating member 83 to slide upwardly.

Figure 4 shows the normally closed limit switch LS2 in its relationship with the actuating member 83 and the switch LS-l, but primarily in its relation to a hydraulic circuit which it electrically controls. The hydraulic circuit system includes a reservoir 132 from which a pump 134 draws hydraulic liquid to circulate it to the opposite ends of each of the four cylinders, one of which is shown at 86. The pump 132 is connected through suitable flow control devices 136, 138 to the upper and lower working chambers in the cylinder and a spring-centered, solenoid valve 140 controls the application and exhaustion of fluid from these chambers to make the cylinders lift or lower the platform 24. The solenoid valve 140 is normally self-centering so as to keep the cylinders 86 idle. However, a pair of solenoid control coils 142 may be selectively energized to shift the valve into opposite operating positions from neutral. The normallyclosed switch LS2 is arranged in circuit with one of the coils 142 so as to trip and to open-circuit that coil and stop the lifting operation of the cylinders 86. To this end the switch actuating member 83 in lifting out of the plane of the paper in Figure 4 wedges its ramp 128 between the rollers 130 on the limit switches so as to separate the rollers. Thereupon the limit switch LS-l is operated and in the next instant the limit switch LS2 is tripped open to deenergize the coil 142, thereby enabling the spring-centered solenoid valve 140 to recenter itself into neutral position and inactivate the cylinders 86 and cause them to remain idle until the switch LS-Z is reclosed.

Figures 5, 6, 7 schematically show the sequence of operation of the machine of the preceding Figures 14. Figure 5 shows the stack S at the instant the lift magnet coils join the rifller magnet coils 65 in becoming energized so as to maintain magnetic fields through the respective magnet cores 63, 61. Immediately the joint field developed by the mutually replsing cores 61, 63 cuts across the top edge of the stack S, the leading edge of the sheets at that corner become polarized so as to repel one another and fan apart much after the action of the pages of a book. This fanning or rifiling action breaks the cohesion between the sheets at that edge and thus the edges of the top four or five sheets mutually separate. Almost immediately as in Figure 6, the top sheet completely separates from the stack and bodily lifts rather evenly and levelly due to the attraction of the lift magnet cores 63 against the undersides of the rollers 68, 70. The frictional engagement between the rotating rollers 70 and the top sheet causes that sheet to pick up motion and move in its own plane toward the pinch rolls 72. In Figure 7 the pinch rolls 72 engage the top sheet to guide it along a path of travel at right angles from the stack from which it was lifted.

A closer study of Figure 7 will reveal two problems occasioned by the sheet moving in the direction from left to right as viewed in Figure 7. In the first place it is noted that the leading edge of the sheet has to negotiate the space immediately above the riffler core 61 after it leaves the last of the magnet rollers 63. The full strength attraction of the core 61 if it remained energized would be such as to deflect the leading edge of the top sheet and draw it downwardly out of line from the path in which it will engage the pinch roller 72. In the second place the lift magnet cores 63 as they are uncovered by the trailing end of the departing sheet are confronted by the next sheet on the top of the stack S which is thereby exposed to a lifting effect to raise it against the rollers 68, 70 as fast as the lift cores 63 are uncovered by the departing sheet. Therefore, instead of the strength of all of the cores 63 being brought to bear simultaneously on the top sheet, they would act in succession to cause the top sheet to rise upwardly in the uneven fashion of a wave or a whip in engaging the undersides of the rollers.

Figure 8 shows a wiring circuit for controlling the electromagnets without bringing into effect the unwanted results of the preceding paragraph and being automatically operated by the limit switches LS-l and LS3. In this circuit, a pair of conductors 144 supply upper and lower branch circuits 146, 148 with current which passes through the common, normally open limit switch LS-1. The upper branch 146 controls an electro-magnetic switch ES-4 which operates the upper branch 150 of a 230 volt D.C. circuit supplied by a pair of conductors 152. The lower branch 148 controls a time-delay switch DS-5 which operates a lower branch 154 in the noted 230 volt, D.C. circuit. The lower branch 154 includes the respective north and south riffler coils 65 which are arranged adjacent the corresponding north and south coils 64 in the lift magnet section. The individual coils 64 for each lift magnet core 63 are connected as a pair in series, but these paired coils are connected in parallel with all other pairs of the coils 64. Suitable trim rheostats 156 and 158 are included in the respective upper and lower branches 150, 154. A jumper load resistor 160 is included in series with the trim rheostat 156 in the upper branch 150 and has a branch 162 which bypasses it under the control of the normally closed limit switch LS3. The limit switch LS3 therefore normally serves to shunt the load resistor 160 by passing current around it through the branch 162. The load resistor 160 is so proportioned with respect to the lift coils 64 that when it is unshunted it tends to reduce the available voltage to the coils by one-half and therefore the coils become energized at only half strength. Inasmuch as the normally closed limit switch LS3 is in the magnet and roller section 22, it is tripped open and introduces the voltage drop of the resistor 160 immediately after the rollers are occupied by a lifted sheet. A time-delay interval on the delay switch DS-5 of approximately onehalf to three-quarters second in duration has been found very satisfactory in one application of the machine.

In the operation of the circuit of Figure 8, the limit switch LS-l is closed upon the predetermined initial movement of the switch actuator 83, Figure 3. Slightly thereafter but practically simultaneously therewith, the limit switch LS2 is tripped open to cause the solenoid valve 140 to be deenergized (Figure 4) and recentered to neutral, whereupon the lift platform temporarily ceases to rise. Simultaneously with the noted closure of the limit switch LS1, the electromagnetic switch ES-4 is brought into operation closing the upper branch circuit 150 to bring the lift coils 64 into energization at full strength. It is noted that the riffier coils 65 are already energized and stand ready to cooperate with the adjacent lift coils owing to the fact that the lower branch circuit 154 is normally maintained closed by the delay switch DS-S. Accordingly, the top sheet bodily lifts through the less than approximately 1" gap thereabove and in the instant that it takes to rise at least two things occur. The depending actuating finger for the limit switch LS3 is moved by the sheet so as to open that switch enabling the load resistor 160 to become effective in the circuit 150. Substantially timed to occur with the delay period being over at this exact point, the delay switch DS-5 open-circuits the lower branch 154- so as to completely deenergize the riffier magnet coils 65 and the magnetism, if any, which remains in the riffier core 61 consists purely of the residual magnetism. In such state with therifiler magnet core 61 deenergized and the lift magnet cores 63 operating at half strength, the top sheet from the stack is brought into frictional engagement with the spinning drive roller and transfers in a direction to the right as viewed in Figure 2 so as to engage the pinch rolls 72. Thereafter this sheet continues to move and vacates the space between the magnet and roller section 22 and the top of the stack S whereupon the switch actuating member 83 (Figure 3) is restored by gravity to its lower position and the limit switch LS3 is released. Accordingly, the limit switch LS-l opens to deenergize the lift magnet coils 64 whereas the delay switch DS-5 immediately recloses to energize the rifiler coils 65, and the normally closed limit switch LS3 recloses to shunt the load resistor 160 and prepares the upper branch circuit for operation of the lift coils 64 at full strength. Also the limit switch LS-2 (Figure 4) recloses to restart the lift cylinders 86 and cause the lift platform 24 to begin to rise and force the top of the stack into contact with the feeler wheel 122 (Figure 3) carried by the switch actuating member 83.

The modification of Figure 9 is the same as the wiring circuit embodied in Figure 8 in all instances where like numerals are used in the two figures. The lift magnets 64 of Figure 9 are normally deenergized as in the prior embodiment and the rifiler coils 65 stay normally energized in a similar fashion. There are two exceptions, however, in that the limit switch LS3 is divided in Figure 9 into two sections, LS3a and LS3b, and the time delay switch of the preceding embodiment is absent and in its stead there is an electro-magnetic switch ES-S. The normally closed limit switch LS3b is included in the shunting branch circuit 162 which is electrically in parallel with the jumper load resistor that bypasses said switch LS-3b when open; the LS3a switch which is likewise normally closed is included in the lower branch 148 of the control circuit. The electro-magnetic switch ES5 is also included in this branch 148 in series with the switch LS-3a and controls the lower branch 154 in the 230 volt D.C. circuit which is supplied with current by the conductors 152. The operation of the modification of Figure 9 follows the same general pattern as the operation of the Figure 8 embodiment. Thus, the lift magnet coils 64 are brought on by the closure of the limit switch LS1 so as to create a magnetic field to lift the top sheet from the stack S. This top sheet engages and accordingly trips the limit switches LS-3a and LS3b to accomplish two functions substantially simultaneously. First the strength of the lift magnet coils 64 is reduced to one-half of their lift value owing to the effective insertion of the now unshunted resistor 160 in the circuit 150 and the LS-3a switch causes the electromagnetic switch ES-S to deenergize and to open-circuit the lower branch 154 so as to deenergize the rifiler coils 65.

It is apparent that the idler rollers 68 in the magnet and roller section 22 have a dual function in providing antifriction coasting engagement with sheets being conveyed therealong and in providing a magnetizable metal path for the field from the salient field coil poles of the lift magnet cores 62. The live rollers 70 which are arranged in tandem in the same section 22, not only provide antifriction engagement with the sheets, but also rotate under torque to frictionally drive them in the direction in which they are to be conveyed. It is appreciated that after the lift coils 64 initially become energized, their magnetic lifting force is first reduced automatically to the part strength magnetic suspending force and that shortly thereafter this suspending force completely collapses at a time before each departing sheet has fully uncovered the remaining stack. The departing sheet naturally sags somewhat under gravity in certain instances and tends to or actually does drag its trailing end against the stack. However, the upper and lower pinch rolls 72 are both in engagement with the leading end or the body portion of the sheet by this time and hold it generally to its horizontal path without actual necessity for further assistance from the electromagnetic coils 64.

Variations within the spirit and scope of the invention described are equally comprehended by the foregoing description.

I claim:

1. In a machine for destacking magnetizable sheets, an upwardly moving support for the stack of sheets, a frame of depending lift members in tandem above the support, a rifiler member disposed slightly below one end of the frame to provide space for a top edge of the stack to intervene between it and the lift member at that end, said lift and rifiler member having coil means to energize them electromagnetically for joint field action in manipulative separation of the sheets, a normally closed first switch in circuit with the riffier coil means to keep it energized, second switches closeable to energize the lift coil means at full strength when the top of the stack approaches said frame, first switching mechanism to open the normally closed first switch for temporarily deenergizing the rifiler coil means when the top sheet completes being magnetically transferred from the stack to the lift members as they draw it to the frame, and second switching mechanism acting substantially simultaneously with the first mechanism to operate at least one of said second switches to reduce the lift coil means to part strength.

2. In a machine for destacking magnetizable sheets, a support for the stack of sheets, a lift magnet frame above the support having tandem arranged lift coils included in a first circuit, means including a riflier magnet coil spaced slightly from one end of the frame to accommodate the top edge of the stack between it and a portion of that end of the lift magnet frame, said lift magnet coils being included in a second circuit, means including switching elements in said first and second circuits effective to reduce or to completely interrupt the energization of the coils, and an actuator engageable by a magnetically 8 attracted sheet from the stack to operate a switching element in the first circuit to fractionally reduce the strength of the lift coils.

3. A machine including an inverted bed of rollers in tandem, means including rows of lift electromagnets extending to at least one end of the bed, a rifiier electromagnet beneath that end of the bed and offset from the adjacent lift electromagnet, means to energize both electromagnets together with the other electromagnets in said rows at full strength to manipulate a sheet upwardly so as to be set in motion by said rollers, and means to substantially simultaneously change the energization of one electromagnet to part strength and deenergize the other.

4. A machine having an inverted bed of rollers in tandem, means for applying torque continuously to disparate ones of the rollers to keep them rotating, lift eleetro magnet, means including a lift electromagnet at one end of the bed, a riffier electromagnet below that end of the bed and offset from said lift electromagnet, said electromagnet means including a lift electromagnet at one end perpendicular planes, and having their corresponding poles confronting one another, means to energize said electromagnets at full strength so that the adjacent ones of their corresponding poles are concurrently of like polarity, and means to substantially simultaneously reduce the energization of the lift electromagnet to part strength and to deenergize said riffler electromagnet.

5. In a sheet handler, a frame having an inverted bed of rollers in tandem, means for applying torque continuously to disparate ones of the rollers to keep them rotating, lift electromagnets mounted to said bed to lift a sheet into contact with the rollers and magnetically hold it in engagement therewith to be frictionally driven as the disparate ones of the rollers rotate, circuit means to impress voltage from a source uniformly at full strength upon the electromagnets, voltage control mechanism in said circuit means effective to initially apply high voltage to the electromagnets to lift a sheet against all rollers in the bed, and a normally full energized rifller magnet below one end of said bed so as to confront the lift electromagnet at that end and so interconnected wth appropriate automatic means to said control mechanism that it has coordinated action with the lift electromagnet aforesaid together with the others, said control mechanism having a control element tripped by each sheet reaching said bed to de-energize said rifller magnet and to immediately reduce the voltage on said electromagnets to a part strength sufficient merely to hold the sheets snugly against the rollers.

6. The method of separating the end ferromagnetic sheet from a group of ferromagnetic sheets by applying a uniform field of magnetic attraction coupled with magnetic repulsion induced between sheets, which includes individually directing a uniform field in the plane of the end sheet while passing a joint field diagonally through a corner of the group until the end sheet has been moved out of its original plane a desired distance, cutting ofi the joint field and said fields having like polarity to cooperatively make the sheets polarize and turn at one edge at that corner, cutting down the uniform field, thus holding the end sheet suspended with substantially all points in a new plane but enabling the other sheets to settle, and removing the suspended sheet in the new plane of the sheet.

7. The method of separating the top ferromagnetic sheet from a stack of ferromagnetic sheets by applying a uniform field of magnetic attraction coupled with magnetic repulsion induced between sheets, which includes individually directing a uniform field downwardly through the plane of the top sheet while passing a joint field diagonally through a top corner of the stack until the top sheet has reached a desired level, said fields having like polarity to cooperatively make the sheets polarize and turn at one edge at that corner, cutting off the joint field and cutting down the uniform field, thus holding the top sheet suspended in a plane at said desired level but enabling the other sheets to settle, and removing the suspended sheet in a path at said level intersecn'ng the path previously taken by the collapsed joint field.

8. Apparatus with control mechanism for automatically separating and successively feeding magnetizable sheets from a supported upright stack of generally horizontal sheets, comprising stack-support reciprocating means to move said stack upwardly, an inverted bed of rollers in tandem to one another in a fixed horizontal location above and in the path of movement of said reciprocating means, means for applying torque continuously to disparate ones of the rollers to keep them rotating, energizable circuit means comprising rows of lift electromagnets extending to at least one end of said bed, normally energized circuit means comprising a riffier electromagnet below and offset beyond that end of the bed so as to confront the adjacent lift electromagnet, stackresponsive first lift circuit control mechanism connected to said stack-support reciprocating means operable by an actuating member to stop the upward progress of said reciprocating means when the stack reaches a predetermined position of proximity to said bed, stack-responsive second lift circuit control mechanism connected to said energizable circuit means operable by an actuating member to continue lifting the top sheet to separate it through a magnetic field from said stack by energizing said lift electromagnets at full strength and magnetically suspending the sheet thereby when lifted into a position to be set in motion against said bed of rollers, and means including single-sheet-responsive control mechanism connected to said normally energized circuit means and to said energizable circuit means operable by actuating means to reduce the strength of said field of the lift elec tromagnets to part strength when the sheet reaches the lifted position aforesaid and to de-energize said riffier magnet.

9. Apparatus according to claim 8 wherein a switchoperating element slidably mounted to said bed constitutes a common operating member for said first and second lift circuit control mechanisms, and wherein a separate switch-operating element mounted to said bed constitutes the actuating means in said single-sheet-responsive control mechanism to reduce the strength of said lift electromagnets to a part strength field and further means de-energizes said rifiler magnet.

References Cited in the file of this patent UNITED STATES PATENTS 2,650,092 Wall Aug. 25, 1953 2,650,824 Fowler Sept. 1, 1953 2,661,208 Fowler Dec. 1, 1953 FOREIGN PATENTS 690,390 Great Britain April 22, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No; 2,895,733 July 21, 1959 Robert B. Powers It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 20, strike out "system for the magnets of the machine; and" 5 column 5, line 9, for "replsing" read repulsing column 8, line 21, for "magnet means including a lift electromagnet at one end" read magnets being U-shaped and being disposed in mutually line 40, for "full" read iullj Signed and sealed this 24th day oi May 1960.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Ofl'lcer 

